Magnetizing Inrush Current Phasor Measurement And Signal Recognition Algorithms

Aiming at the problem of inrush current identification,the scheme of inrush current identification based on phasor data is widely used in engineering.However,with the change of power grid operation conditions,there are many limitations in phasor data acquisition and inrush current identification,which affect the accurate identification of inrush current,and then affect the correct blocking of protection,resulting in protection disoperation / refusal to operate.On the one hand,the acquisition of phasor data depends on the phasor measurement algorithm.However,the dynamic change of current signal during inrush current generation,including second harmonic,decaying DC and other frequency components,leads to a sharp decline in the accuracy of phasor measurement algorithm,which can not provide accurate phasor data for inrush current identification algorithm;on the other hand,with the improvement of transformer material and rated operating point,the second harmonic content in inrush current decreases,The ability of traditional inrush current identification based on the second harmonic braking principle is reduced.Therefore,in order to realize the accurate identification of inrush current,this paper focuses on the measurement algorithm of inrush current phasor based on the time-domain information and frequency-domain information.The main work of this paper is as followsConsidering that the existing phasor models do not fully consider the electrical characteristics of inrush current and the modeling is incomplete,this paper first describes the generation mechanism of inrush current,and analyzes the frequency components and dynamic characteristics of inrush current;based on the analysis results,the phasor model of inrush current signal decomposition representing frequency components and Taylor phase expansion representing dynamic characteristics are established The phasor model takes into account the effects of fundamental,second harmonic and decaying DC components of inrush current,and fully expresses the key electrical characteristics of inrush current.Based on the Taylor expansion phasor model of inrush current,the time domain phasor measurement algorithm TEIC is proposed,which can effectively filter the influence of decaying DC,second harmonic and noise,and obtain accurate phasor data.On this basis,in order to shorten the inherent time delay of the algorithm and improve the dynamic response performance,the FPEIC algorithm using frequency domain information is studied.Firstly,the fundamental,second harmonic and attenuated DC filters are established based on the Fourier transform,and the phasor estimation values under different filtering frequencies in a sampling window are obtained,and the solving equations are established.Secondly,the off-line coefficients are calculated according to different filtering frequencies The corresponding coefficient matrix is found in the table;then,the coefficient matrix and the estimated value of phasor are substituted into the solving equation to calculate the Taylor coefficient and get the accurate phasor data;finally,through the verification of MATLAB ideal signal,PSCAD /EMTDC simulation signal and field measured data,it is proved that FPEIC algorithm can reduce 200% of the same algorithm in obtaining accurate phasor data of inrush current The response time of more than MS is more suitable for the engineering application of inrush current identification.Based on the phasor model of inrush current signal decomposition,a method of inrush current identification is proposed,which is suitable for the case of low second harmonic content.Firstly,the phasor model is reconstructed as amplitude / phase angle model,and the expression of the second-order Taylor coefficient in the model is obtained by Taylor series expansion.Secondly,the mechanism and variation law of the coefficient under inrush current and fault conditions are studied,and it is proved that the second-order Taylor coefficient can represent the electrical characteristics of the signal,such as the second harmonic content and the fundamental wave attenuation speed,and the inrush current identification model is established based on it.The simulation results show that the proposed algorithm can identify inrush current quickly and accurately,and has the ability to resist 35 d B noise,which can effectively avoid false short-term blocking protection.